This thesis describes the preparation and properties of some methyleneamino derivatives of boron, magnesium and aluminium. The structural implications of their I.R. and (L^) H n.m.r. spectra are discussed. As a background to the work, the characteristics of such compounds are discussed and a survey of methyleneamino derivatives of metals and metalloids is presented. Bis (di-t-butylmethyleneamino) fluoroborane. ((^t) Bu (_2) C: N) (_2) BF, was prepared from borom trifluoride and di-t-butylmethyleneminolithium and used to synthesise and three compounds ((^t) Bu (_2) C: N) (_3) B, (^t) Bu (_2) C: NBF (_2) and ((^t) Bu (_2) C: N) (_2) BH. Several compounds in which boron is in a heterocyclic ring system, (^t) Bu (_2) c: NB (^X) – (^Y) – (_Y) – (_X) and two alkyl (di-t-butylmethyleneminolithium) boranes, (^t) Bu (_2) C: NB (^t) Bu (_2) and ((^t) Bu (_2) C: N) (_2) BMe, have been prepared. The I.r and (^1) H n.m.r spectra of these new di-t-butylmethyleneminolithium, ((^t) Bu (_2) C: N) (_n) BX (_3-n), are consistent with there c=n=b skeletons being linear as appropriate for significant n → b dative N-bonding. The new methyleneaminomagnesium compounds are of the following formula types: [R (_2) c: nmGx], [(R (_2) C: N) (_2) Mg] (_n), R (_2) C: NMgBr. 2THF, LiMg (N: CPh (_2)) (_3) OEt (_2)) (_4). The associated species (n usually = 2) are believed to co-ordinate via bridging methyleneamino groups. The I.R spectra of compounds containing terminal methyleneamino groups are consistent with the C.N.Mg units being effectively linear. The preparation of the tris (di-t-butylmethyleneminolithium) alane, ((^t) Bu (_2) C: N) (_3) Al, from aluminium hydride and di-t-butylmethyleneminolithium has been shown to be more reliable than the reaction between aluminium trichloride and iminolithium. Similar reactions o prepare mono and bis (imino) akanes were less successful, and only once could a bis (imino) alane be isolated as a trimethylamine adduct, ((^t) Bu (_2) C: N) (_2) AlH. NNMe (_3). The I.R and (^l) H n.m.r. spectra of these two compounds indicate that their c=n=Al units are effectively linear, as appropriate for N → Al dative N- Bonding. Preliminary studies of reactions between several methylaluminium compounds and di-t-butylmethyleneminolithium or its lithio derivative have been made. The preparation and properties of di-t-butylmethyleneminolithium, (^t) Bu (_2) C: NNMe (_2), are discussed boron compounds and tetramethylguanidine or its lithio derivative are described in Appendix 2. The experimental techniques used in this research are described in Appendix 3.